Dual purpose coil for automobile starter motors

ABSTRACT

A dual purpose coil is disclosed for use as both a solenoid and as one of the field coils of an automobile starter motor, the coils being disposed in a housing about an armature. The dual purpose coil has a movable motor pole associated with it which is normally spring biased apart from the coil. When initial current flows through the coil, the pole is pulled into position in the center of the coil, and such motion causes a starter drive gear assembly, which is clutched to the armature for rotation thereby, to engage the flywheel of the automobile engine. As soon as the pole is pulled-in, a switch is opened to direct current through all of the field coils, including the dual purpose coil, thereby causing rotation of the motor armature and gear assembly to crank the automobile engine. The dual purpose coil is defined by only a single conductive winding of predetermined turns and dimensions which operates not only to pull-in the pole during initial current flow therethrough, but additionally to hold-in the pole during current flow through all of the coils.

United States Patent 191 Erwin, Jr.

Jan. 2, 1973 54 DUAL PURPOSE COIL FOR AUTOMOBILE STARTER MOTORS [75] Inventor: Henry P. Erwin, Jr., Pasadena,

Calif.

[73] Assignee: Precision Field. Coil Company,

' Venice, Calif.

[22] Filed: March 25, 1971 ,[21] Appl. No.: 127,928

Primary Examiner-G. R. Simmons AttorneyChristie, Parker & Hale ABSTRACT A dual purpose coil is disclosed for use as both a solenoid and as oneof the field coils of an automobile starter motor, the coils being disposed in a housing about an armature. The dual purpose coil has a movable motor pole associated with it which is normally spring biased apart from the coil. When initial current flows through the coil, the pole is pulled into position in the center of the coil, and such motion causes a starter drive gear assembly, which is clutched to the armature for rotation thereby, to engage the flywheel of the automobile engine. As soon as the pole is pulled-in, a switch is opened to direct current through all of the field coils, including the dual purpose coil, thereby causing rotation of the motor armature and gear assembly to crank the automobile engine. The

2 Claims, 4 Drawing Figures PATENTEDm 2cm 3.708.682

' sum 1 OF 2 DUAL PURPOSE COIL FOR AUTOMOBILE STARTER MOTORS BACKGROUND OF THE INVENTION This invention relates to automobile starter motors and, more particularly, to such motors utilizing a dual purpose coil to act both as a solenoid and as one of the field coils.

Automobile starter motors using dual purpose coils are known and are presently marketed by the Ford Motor Company. These motors have a housing in which is disposed a rotary motor armature and a plurality of field coils positioned about the armature for effecting rotation of the armature in response to current flow through the coils. One of the coils serves also as a solenoid to selectively pull-into the center thereof, through a hole in the housing, a movable starter motor pole which is hinged to the housing; the movable pole moves in response to an initial flow of current through this one coil.

These motors further include a drive gear assembly mounted on the armature shaft for rotation therewith and for movement axially along the armature shaft. Means cooperate with the hinged pole for controlling the position of the drive gear assembly along the armature shaft for selective engagement of the drive gear as sembly with an engine flywheel in a conventional manner. When the hinged pole is pulled-into-the dual purpose coil, the drive gear assembly engages the flywheel. Current is then directed through all the field coils, including the dual-purpose coil which then acts as a field coil and as a solenoid, thereby causing rotation of the motor armature and drive gearassembly to crank the engine via the flywheel. When the engine starts, current flow through the coils is cut off thereby retracting the drive assembly and turning off the starter motor and allowing the drive gear assembly to retract along the starter motor shaft from the engine flywheel.

It was found that the prior dual purpose coil, although performing well as a field coil, did not function properly as a solenoid. More specifically, in acting as a solenoid, the coil must perform two functions: 1) it must pull-in" the movable'field pole during initial current flow therethrough'and (2) it must hold-in the movable field pole during subsequent current flow through all of the coils.

The dual purpose coil operates as a solenoid since the current flowing through it'creates a magnetic field which attracts the movable field pole into the center of the coil, the magnetic field strength being a function of the product of the number of turns of the coil winding and the magnitude of current flow therethrough. With this type of starter, when the ignition key is turned, all the voltage from the battery is applied across the dual purpose coil which causes a significant current to flow therethrough, thereby developing a very strong magnetic field effective to pull-in the movable field pole.

When the movable field pole is pulled-in, it opens a switch to open a shunt across the other field coils and permit current to flow through all of the coils so that the armature may be caused to rotate in accordance with known principles of DC motors. This current has a magnitude less'than the initial current flow through the dual-purpose coil because of the increased impedance of the added coils. Thus, the magnetic field strength developed by the dual purpose coil is reduced when current is directed through all of the coils. It was discovered that this weaker magnetic field, although adequately contributing to armature rotation, was not sufficient to hold-in the field pole and the latter began to periodically slip out. Movement of the movable pole out of its operative position re-established the shunt and also produced retraction of the drive gear from the flywheel, thus causing the starter motor to operate intermittently, or to chatter.

' In an effort to solve this problem, a dual-purpose coil was developed having two separate windings. One winding was termed the pull-in winding and was fabricated of relatively heavy wire with relatively few turns. This winding functioned properly to initially pullin the pole. The second winding was light-weight wire of small diameter having many turns. This second winding was termed the hold-in" winding for it effectively prevented periodic slippage of the field pole out of its position within the center of the coil.

More specifically, the hold-in winding of these other prior dual purpose coils was generally connected in series between the larger pull-in winding and ground. During the initial pull-in stage, current flowed only through the pull-in winding since the switch was closed to establish a shunt path from the pull-in winding to ground thereby by-passing the hold-in winding and the other field coils. When the movable field pole was pulled-in, thereby opening the switch, current was made to flow through the hold-in winding. This current, although much less in magnitude than that flowing through the pull-in winding because of the lessercrosssectional area of the hold-in winding, cooperated with the large number of turns to define a magnetic field strength sufficient to hold in the field pole.

After dual purpose coils having the two separate pull-in and hold-in windings were used for a while, it was discovered that the hold-in winding burned out if the engine was cranked for a long while before actually starting. Once hold-in winding burned out, the field pole associated with the dual purpose coil began to periodically slip out because of the weaker magnetic field, and the problem of starter motor chatter was again encountered.

SUMMARY OF THE INVENTION The present invention, recognizing the above problems and drawbacks, provides a dual purpose coil capable of performing both pull-in and hold-in functions for the normal life of the coil. There is no danger of a hold-in winding burning out during excessive engine cranking since such a winding is not used, nor is it required or necessary.

Basically, the dual purpose coil of the present invention consists of a single conductive winding of predetermined dimensions and turns'which operates both to pull-in the movable fieldpole during an initial current flow through the coil and to hold-in the field pole during subsequent current flow through all of the field coils. In other words, the dimensions and number of turns of this single winding are such that the ampturns (magnetic field strength) developed thereby is sufficient to pull-in the field pole when the current is relatively great and is sufficient to hold-in the field pole even during current flow of a lesser magnitude as when current flows through all the field coils. In in a preferred embodiment, the single winding of the dual purpose coil has approximately twice as many turns as the pull-in winding of the prior art. Its cross-sectional area is less than such prior art winding, thereby increasing the resistance and lowering the permissible current flow. However, in terms of magnetic field strength, the increased turns more than compensates for the decreased current flow by developing a magnetic field strength significantly greater than that developed by the prior art pull-in winding alone, or by a combination of the latter winding and the prior art hold-in winding. This significance is most apparent during current flow through all the field coils when the current flowing through the dual purpose coil is less in magnitude than the initial pull-in current. In this mode, the number of turns causes a magnetic field to be developed which is more than sufficient to hold-in the field pole, such magnetic field also serving to develop part of the necessary torque for armature rotation.

BRIEF DESCRIPTION OF TI-IEDRAWING These and other aspects and advantages of the present invention are more clearly described with reference to the accompanying drawing wherein:

FIG. 1 is a perspective cutaway view of an automobile starter motor embodying the principles of the present invention;

FIG. 2 is a schematic representation of the field coils used in the motor of FIG. 1 with the-dual purpose coil shown partly in a cutaway view;

FIG. 3 is a typical prior art double winding dual-purpose coil; and I FIG. 4 is a schematic diagram of the motor circuitry used in the arrangement of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT An automobile starter motor embodying the principles 'of this invention is described with reference to FIGS. 1, 2 and 4. As a whole, the motor is a conventional four-pole DC motor commonly used on Ford Falcon automobiles. The motor includes a cylindrical housing 12 in which is contained a conventional commutator/armature assembly 13 (hereinafter referred to as the armature). Generally speaking, and'in a manner more fully described below, the armature is defined about a shaft 14 which is made to rotate in response to g the flow of current through four field coils l6, 18,

and 22 mounted within the housing in quadrature about the armature.

Referring specifically to FIGS. 2 and 4, the field coils are connected together in what is termed a series/parallel. connection. An outer end 24 of coil 16 and an outer end 26 of coil 22 are each connected through a junction 41 to the positive terminal 43 of a l2-volt automobile battery (not shown). An inner end 28 of coil 16 is connected to an inner end 30 of coil 20, an outer end 32 of which is connected to an inner end 34 of coil 18, an outer end 36 of which is connected to an inner end 38 of coil 22. A junction point 40 represents the junction between outer end 32 of coil 20 and inner end 34 of coil 18.

Each of field coils 18, 20 and 22 has an associated field pole (not shown) which is fixedly mounted within I housing 12 and positioned within the center opening of the coil. Coil 16, when operating as a field coil, also has a field pole 50 positioned in the center thereof. The uniqueness of coil 16 and field pole 50 form the basis of this invention and are explained in greater detail below. With reference to FIG. 4, a pair of graphite brushes 42 and 44 are connected to junction point 40 and are disposed at opposite sides of the armature. These brushes are hereinafter referred to as the hot brushes since they are connected directly to the battery through the coils. An additional pair of graphite brushes 46 and 48 are each grounded and are positioned on opposite sides of armature 13 in quadrature with brushes 42 and 44. The significance of the brushes is explained below.

When current is directed to flow through all four coils in a manner also explained below, it follows two separate serial paths which are themselves defined in parallel. A first current path A is defined from junction 41 through coils 16 and 20 in series to hot brush 44 through junction 40. A second current path B is defined from junction 41 through coils 22 and 18 in series to hot brush 42 through junction 40.

It is well known, under general principles of DC motors, that when all four coils operate as field coils, the current flow through the coils along paths A and B sets up a magnetic field about the armature which produces a counterclockwise torque contributing in part to a corresponding rotation of the armature. Additional torque to cause armature rotation is produced by the flow of current into and out of a number of conductors (not clearly shown) embedded in longitudinal slotsin the surface of the armature. Current is led into and out of these conductors when the hot brushes make contact with the commutator portion of the armature. The commutator maintains a predetermined current flow path through the conductors such that the magnetic field developed as current flows through each conductor defines a counterclockwise torque on the armature to assist the torque developed by the field coil.

Coil 16 is used not only as afield coil, but as a solenoid as well. In this sense it is sometimes referred to as a dual-purpose coil. By way of explanation, field pole 50 is generally carried by a lever arm-52 on the underside thereof. Lever arm 52 forms part of a control assembly 54 which is 'of unitary construction and is hinged at one end of arm 52 to the outer surface of housing 12 by means of a hinge bracket 56. A hinge pin 58 is positioned through aligned holes (not shown) in assembly 54 and the bracket. The other segment of assembly 54 is comprised of a fork'60 having one end defined essentially at hinge pin 58 and a forked end (not shown) extending on opposite sides of a drive gear assembly 62 slidably mounted on armature shaft 14 for rotation therewith, but yet selectively movable along the axis of the shaft.

Drive gear assembly 62 includes a gear 64 for engaging a corresponding gear (not shown) on a flywheel (not shown) of an automobile engine with which starter motor 10 is used. Assembly 62 further includes a clutch 66 for providing engagement between the two gears when the drive assembly is moved toward the flywheel and for preventing the flywheel from driving the starter motor after the engine starts. Mounted to drive assembly 62 are a pair of lips (not shown) extending on opposite sides thereof. The forked end of fork 60 is designed to engage these lips to control the axial position of gear 64 along armature shaft 14. More specifically, as fork 60 is pivoted forwardly about hinge pin 58, the forked end will push against the lips of drive assembly 62, thereby moving the assembly forward along the armature shaft until gear 64 engages the flywheel.

The pivotal position of fork 60, and thus the axial position of gear 64, is controlled by the position of pole piece 50 mounted to lever 'arm 52. Fork 60 is normally biased rearwardly in the position shown in FIG. I by the action of a compression spring 68 fixed between housing 12 and the fork. In the normal rearward position of fork 60, lever arm 52 is correspondingly inclined upwardly at a free end 74, thereby keeping pole piece 50 out of the center of coil 16, there being an aperture 70 formed through the housing to accommodate the pole piece when the lever arm is pulled down.

A normally closed switch 72 is defined in part by a leaf spring 73 which is mounted on the outer surface of the housing adjacent free end 74 of lever arm 52. As best shown in FIG. 4, one terminal 76 of switch 72 is connected electrically to a junction point 78 representing the junction of inner end 28 of coil 16 and inner end 30 of coil 20. Another terminal 80 of switch 72 is grounded. A pair of contacts 82 and 84 are normally biased in contact with each other due to the normally biased state of the spring. In this state, a circuit path is defined from junction 78 to ground thereby enabling currentto flow from the battery through only coil 16 and then to ground. No current flows through the other coils.

Spring switch 72 is physically depressed, thereby breaking contact between the two contacts, when current initially flows through coil 16, which occurs when the ignition key (not shown) is turned thereby connecting the battery to the outer ends of coils 16 and 22. This initial flow of current sets up a magnetic field about coil 16 which is of sufficient strength to overcome the bias established by spring 68 and to force lever arm 52 down,'thereby positioning pole piece 50 within aperture 70.

Lever arm has a lug 86 which extends out beyond the boundary of pole piece 50. Lug 86'is designed to engage and depress spring 72 when lever arm 52 is pulled-in by the magnetic field induced about coil 16. When this happens, switch 72 opens thereby allowing current to flow through all the motor field coils, thereby causing rotation of the armature. In addition, when lever arm 52 is pulled down, fork 60 is moved forwardly thereby pushing starter drive assembly 62 forwardly on armature shaft 14 until gear 64 engages a flywheel. In this manner the automobile engine, not shown, may be cranked. I

It is clear, therefore, that coil 16 performs two main function: (1) it first operates solely as a solenoid during initial current flow therethrough to pull-in pole piece 50, thereby moving starter drive assembly 62 into engagement with a flywheel; and (2) it then operates both as a field coil, during subsequent current flow through all the coils to effect rotation of the armature, and as a solenoid to hold-in pole piece 50 during cranking. Thus, coil 16, in order to properly function as a solenoidQmust not only include means for pulling-in pole piece 50, but additionally must include means for holding-in the field pole during current flow through all the coils when the current flow through coil 16 is reduced.

A typical prior art coil 88 (FIG. 3) was developed to satisfy the above requirements and it was, and still is, used on motors like motor 10. Coil 88 is fabricated with two windings: (1) a pull-in winding 90 of relatively large cross-sectional area and few turns; and (2) a holdin winding 92 of relatively small cross-sectional area and having many turns. During current flow through all the coils, the magnetic field developed about winding 92 is of sufficient strength to supplement that developed by winding 90 so that the field pole is continuously maintained in the center of the coil.

With reference now to FIG. 3, and with regard to one scale of starter motor 10 used in large-engined Ford Falcons, prior art coil 88 had a seven-turn pull-in winding 90 with a cross-sectional area of approximately 0.01 in. It also had a l00-turn hold-in winding with a cross-sectional area of approximately 0.0002 in. During the initial pull-in stage, current flowed only through winding 90 since winding 92 was shunted by the circuit path through switch 72 to ground; with reference to FIG. 4, winding 92 was connected between junction 78 and ground in the prior art.

The initial current flow through pull-in winding 90 was approximately 300 amps which produced a magnetic field strength of 2,100 amp-turns. This magnetic field sufficiently overcame the bias of spring 68 to pull down the field pole and thus lever arm 52 as well. Lugs 86 then depressed and opened switch 72 to allow current to flow through winding 92, as well as the other field coils. The current through winding 90 was thus reduced to approximately amps by reason of the increased resistance of the added coils. Even though the current through winding 92 was only 4-5 amps because of its much smaller area, 400-500 ampturns were developed to define a secondary magnetic field of a strength sufficient, when added to that developed by winding 90 along, to hold-in the field pole. Notwithstanding the benefits of a separate hold-in winding, it suffered from a serious disadvantage in that it burns out during excessive engine cranking.

Single winding 25 of coil 16, on'the other hand, never burns out. It is preferably designed with about 14 turns and a cross-sectional area of about 0.0084 in when it is to be used in the particular Ford starter motor above-described. Although the current initially flowing through coil 16 with switch 72 closed is 220 amps, as opposed to 300 amps (due to the smaller area and longer length of the winding), the increased turns more than makes up for the lower current thereby providing more than adequate pull-in power. Addi tionally, when only 90 amps flow therethrough when switch 72 is open, the increased turns of winding 25 relative to coil 88 provides sufficient magnetic field strength to hold-in the field pole so that starter drive assembly 62 is engaged with the flywheel.

It is to be noted that winding 25 of coil 16 differs substantially from the single windings defining coils 18,20 and 22. For instance, the single windings of coils 18, 20 and 22 each have a greater cross-sectional area than that of coil 16 and may have fewer turns than coil, 16. Coils 18, 20 and 22 serve only as field coils to effect rotation of the armature and thus do not have to develop the substantial pull-in magnetic strength required by coil 16 when acting only as a solenoid and the hold-in magnetic strength required when coil 16 acts as both a field coil and a solenoid. In the embodiment presented here for illustration, each of coils 18, 20 and 22 has a single winding of eight turns and of 0.01 in cross-sectional area.

Coil 16 has been defined with regard to a starter motor 10 used on Ford Falcons with a relatively large engine therein. If a smaller engine were used, a correspondingly smaller starter motor would be employed. This motor would be essentially identical to that of motor 10; but only scaled down in size in all respects. Thus, the dimensions and turns of the dual purpose coil used in such a smaller motor might produce a weaker magnetic field than coil 16 of motor 10, but such field would nonetheless perform the necessary pull-in and hold-in functions because of the scaled down dimensions, weights and other related characteristics of the other structural elements of the motor.

in fact, all that is required in any dual purpose coil according to this invention is that it be defined by a single winding which, when taking into account the nature and characteristics of the field pole, control assembly, spring 68 and starter drive 62, etc., provides an adequate magnetic field strengthto both pull-in the field pole during initial current flow therethrough and hold-in the pole during subsequent current flow through all the coils.

g It must be reiterated that even though single winding coils have been used before as so-called dual purpose" coils, they failed to effectively function as solenoids when simultaneously operating as a field coil because they did not generate sufficient hold-in magnetic field strength. Use of the separate hold-in winding was introduced to remedy that disadvantage. This invention recognizes that a single winding should nonetheless be used for the reasons above described.

The actual dimensions and number of turns of this single winding may be determined through individual experimentation. All that is important is that whatever dimensions and turns are chosen, the single winding function properly as a solenoid while also operating as a field coil.

Therefore, although the invention has been described with regard to a specific starter motor having a dual purposecoil of specific dimensions and turns, numerous modifications and alterations may be made thereto, consistent with the above requirements, without departing from the spirit of the invention as defined in the following claims.

What is claimed is:

1-. In an automobile, starter motor having a housing in which is disposed an armature and a plurality of field coils'positioned at corresponding stations about the armature for effecting rotation of the armature in response to current flow through the coils, the coil at one of the stations also serving, in response to an initial flow of current through said one coil, as a solenoid to selectively pull into the center thereof and through a hole in the housing, a pole hinged to the housing, the motor further having a starter drive assembly coupled to the armature for rotation therewith and means cooperating with the hinged pole for controlling the position of the starter drive assembly axially of themmature, the improvement comprising:

a single conductive winding formed of a single length of wire of predetermined dimensions and turns defining the coil at said one station, the winding defining a current flow path at said one station for flow therethrough of initial pull-in current effective to pull-in the hinged pole and, in cooperation with the remaining coils of said plurality, for flow therethrough of hold-in current effective to holdin the hinged pole during current flow through the coils at all of the stations without chatter of the hinged pole during operation of the motor under no-load conditions, the winding being connected to the other coils so that the current flow path at the one station during flow of pull-in current is the same as during flow of hold-in current.'

2. In an automobile starter motor having a housing in which is disposed an armature and a plurality of field coils positionedabout the armature for effecting rotation of the armature in response to current flow through the coils, one of the coils also serving, in response to an initial flow of current through said one coil, as a solenoid to selectively pull into the center thereof and through a hole in the housing, a pole hinged to the housing, the motor further having a starter drive assembly coupled to the armature for rotation therewith and means cooperating with the hinged pole for controlling the position of the starter drive assembly axially of the armature, the improvement comprising; v

a single conductive winding of a single length of wire having a cross-sectional area of about 0.0084 in. and about 14 turns serving as said one coil and operating both to pull-in the hinged pole during the initial flow of current therethrough and, in cooperation with the remaining coils of said plurality, to hold-in the hinged pole during current flow through all of the coils without chatter of the hinged pole during operation of the motor under no-load conditions. 

1. In an automobile starter motor having a housing in which is disposed an armature and a plurality of field coils positioned at corresponding stations about the armature for effecting rotation of the armature in response to current flow through the coils, the coil at one of the stations also serving, in response to an initial flow of current through said one coil, as a solenoid to selectively pull into the center thereof and through a hole in the housing, a pole hinged to the housing, the motor further having a starter drive assembly coupled to the armature for rotation therewith and means cooperating with the hinged pole for controlling the position of the starter drive assembly axially of the armature, the improvement comprising: a single conductive winding formed of a single length of wire of predetermined dimensions and turns defining the coil at said one station, the winding defining a current flow path at said one station for flow therethrough of initial pull-in current effective to pull-in the hinged pole and, in cooperation with the remaining coils of said plurality, for flow therethrough of hold-in current effective to hold-in the hinged pole during current flow through the coils at all of the stations without chatter of the hinged pole during operation of the motor under no-load conditions, the winding being connected to the other coils so that the current flow path at the one station during flow of pull-in current is the same as during flow of hold-in current.
 2. In an automobile starter motor having a housing in which is disposed an armature and a plurality of field coils positioned about the armature for effecting rotation of the armature in response to current flow through the coils, one of the coils also serving, in response to an initial flow of current through said one coil, as a solenoid to selectively pull into the center thereof and through a hole in the housing, a pole hinged to the housing, the motor further having a starter drive assembly coupled to the armature for rotation therewith and means cooperating with the hinged pole for controlling the position of the starter drive assembly axially of the armature, the improvement comprising: a single conductive winding of a single length of wire having a cross-sectional area of about 0.0084 in.2 and about 14 turns serving as said one coil and operating both to pull-in the hinged pole during the initial flow of current therethrough and, in cooperation with the remaining coils of said plurality, to hold-in the hinged pole during current flow through all of the coils without chatter of the hinged pole during operation of the motor under no-load conditions. 